False FPS

[bertelschmitt]

VideoCaptureStreamRT consistently reports double the actual fps. For an 8 fps stream, it reports 16 fps.
As a baseline, here is the ffprobe output for the stream under test:

  Metadata:
    title           : Session streamed by "preview"
  Duration: N/A, start: 0.000000, bitrate: N/A
  Stream #0:0: Video: h264 (High), yuv420p(progressive), 2304x1296, 8 fps, 16 tbr, 90k tbn
  Stream #0:1: Audio: aac (LC), 16000 Hz, mono, fltp

8 fps is correct.

For the same stream, VideoCaptureStreamRT says the vid.fps is 16 fps.
It comes to that conclusion from reading the r_frame_rate of the vinfo dict:

vinfo: {'index': 0, 'codec_name': 'h264', 'codec_long_name': 'H.264 / AVC / MPEG-4 AVC / MPEG-4 part 10', 'profile': 'High', 'codec_type': 'video', 'codec_tag_string': '[0][0][0][0]', 'codec_tag': '0x0000', 'width': 2304, 'height': 1296, 'coded_width': 2304, 'coded_height': 1296, 'closed_captions': 0, 'film_grain': 0, 'has_b_frames': 0, 'pix_fmt': 'yuv420p', 'level': 51, 'chroma_location': 'left', 'field_order': 'progressive', 'refs': 1, 'is_avc': 'false', 'nal_length_size': '0', 'r_frame_rate': '16/1', 'avg_frame_rate': '0/0', 'time_base': '1/90000', 'bits_per_raw_sample': '8', 'extradata_size': 24, 'disposition': {'default': 0, 'dub': 0, 'original': 0, 'comment': 0, 'lyrics': 0, 'karaoke': 0, 'forced': 0, 'hearing_impaired': 0, 'visual_impaired': 0, 'clean_effects': 0, 'attached_pic': 0, 'timed_thumbnails': 0, 'captions': 0, 'descriptions': 0, 'metadata': 0, 'dependent': 0, 'still_image': 0}}

To produce the proper 8fps, I changed the following line in stream_info.py
def get_info(stream_url, timeout=None, duration_ms: int = 100):

To this line:
def get_info(stream_url, timeout=None, duration_ms: int = 1000):

Now the vinfo dict reads as follows:

vinfo: {'index': 0, 'codec_name': 'h264', 'codec_long_name': 'H.264 / AVC / MPEG-4 AVC / MPEG-4 part 10', 'profile': 'High', 'codec_type': 'video', 'codec_tag_string': '[0][0][0][0]', 'codec_tag': '0x0000', 'width': 2304, 'height': 1296, 'coded_width': 2304, 'coded_height': 1296, 'closed_captions': 0, 'film_grain': 0, 'has_b_frames': 0, 'pix_fmt': 'yuv420p', 'level': 51, 'chroma_location': 'left', 'field_order': 'progressive', 'refs': 1, 'is_avc': 'false', 'nal_length_size': '0', r_frame_rate': '16/1', 'avg_frame_rate': '8/1', 'time_base': '1/90000', 'start_pts': 9808, 'start_time': '0.108978', 'bits_per_raw_sample': '8', 'extradata_size': 24, 'disposition': {'default': 0, 'dub': 0, 'original': 0, 'comment': 0, 'lyrics': 0, 'karaoke': 0, 'forced': 0, 'hearing_impaired': 0, 'visual_impaired': 0, 'clean_effects': 0, 'attached_pic': 0, 'timed_thumbnails': 0, 'captions': 0, 'descriptions': 0, 'metadata': 0, 'dependent': 0, 'still_image': 0}}

If you now take avg_frame_rate instead of r_frame_rate, you get the correct 8 fps frame rate of the stream.

[chenxinfeng4]

Thanks for your advisement. Please try this version, I'll release in PYPI next time.

pip install -U https://github.com/chenxinfeng4/ffmpegcv.git

[bertelschmitt]

Sorry, bu hao: Collecting https://github.com/chenxinfeng4/ffmpegcv.git Downloading https://github.com/chenxinfeng4/ffmpegcv.git - 403.2 kB 41.4 MB/s 0:00:00 ERROR: Cannot unpack file /tmp/pip-unpack-8c02ileu/ffmpegcv.git (downloaded from /tmp/pip-req-build-r5m_jxin, content-type: text/html; charset=utf-8); cannot detect archive format ERROR: Cannot determine archive format of /tmp/pip-req-build-r5m_jxin B From: ChenXF ***@***.***> Sent: Friday, May 30, 2025 16:02 To: chenxinfeng4/ffmpegcv ***@***.***> Cc: bertelschmitt ***@***.***>; Author ***@***.***> Subject: Re: [chenxinfeng4/ffmpegcv] False FPS (Issue #70) <https://avatars.githubusercontent.com/u/17546446?s=20&v=4> chenxinfeng4 left a comment (chenxinfeng4/ffmpegcv#70) <#70 (comment)> Thanks for your advisement. Please try this version, I'll release in PYPI next time. pip install -U https://github.com/chenxinfeng4/ffmpegcv.git — Reply to this email directly, view it on GitHub <#70 (comment)> , or unsubscribe <https://github.com/notifications/unsubscribe-auth/AMCPYCTSYJ2JNFCTCVK3GBT3A7677AVCNFSM6AAAAAB5743XLKVHI2DSMVQWIX3LMV43OSLTON2WKQ3PNVWWK3TUHMZDSMRRGQYTSOBTHA> . You are receiving this because you authored the thread. <https://github.com/notifications/beacon/AMCPYCQP7ZKRVKKUAZ33AE33A7677A5CNFSM6AAAAAB5743XLKWGG33NNVSW45C7OR4XAZNMJFZXG5LFINXW23LFNZ2KUY3PNVWWK3TUL5UWJTVOEFKD4.gif> Message ID: ***@***.*** ***@***.***> >

[bertelschmitt]

Assuming that ffmpeg_reader.py is the one with the change, I installed it manually. But it did not fix the problem. My fix is in stream_info.py and it goes like this: def get_info(stream_url, timeout=None, duration_ms: int = 1000): rtsp_opt = '' if not stream_url.startswith('rtsp://') else '-rtsp_flags prefer_tcp -pkt_size 736 ' analyze_duration = f'-analyzeduration {duration_ms * 1000}' cmd = (f'ffprobe -v quiet -print_format json=compact=1 {rtsp_opt} {analyze_duration} ' f'-select_streams v:0 -show_format -show_streams "{stream_url}"') output = subprocess.check_output(shlex.split(cmd), shell=False, timeout=timeout) data: dict = json.loads(output) vinfo: dict = data['streams'][0] StreamInfo = namedtuple( "StreamInfo", ["width", "height", "fps", "count", "codec", "duration"] ) outinfo = dict() outinfo["width"] = int(vinfo["width"]) outinfo["height"] = int(vinfo["height"]) #outinfo["fps"] = eval(vinfo["r_frame_rate"]) outinfo["fps"] = eval(vinfo["avg_frame_rate"]) ##fix B From: ChenXF ***@***.***> Sent: Friday, May 30, 2025 16:02 To: chenxinfeng4/ffmpegcv ***@***.***> Cc: bertelschmitt ***@***.***>; Author ***@***.***> Subject: Re: [chenxinfeng4/ffmpegcv] False FPS (Issue #70) <https://avatars.githubusercontent.com/u/17546446?s=20&v=4> chenxinfeng4 left a comment (chenxinfeng4/ffmpegcv#70) <#70 (comment)> Thanks for your advisement. Please try this version, I'll release in PYPI next time. pip install -U https://github.com/chenxinfeng4/ffmpegcv.git — Reply to this email directly, view it on GitHub <#70 (comment)> , or unsubscribe <https://github.com/notifications/unsubscribe-auth/AMCPYCTSYJ2JNFCTCVK3GBT3A7677AVCNFSM6AAAAAB5743XLKVHI2DSMVQWIX3LMV43OSLTON2WKQ3PNVWWK3TUHMZDSMRRGQYTSOBTHA> . You are receiving this because you authored the thread. <https://github.com/notifications/beacon/AMCPYCQP7ZKRVKKUAZ33AE33A7677A5CNFSM6AAAAAB5743XLKWGG33NNVSW45C7OR4XAZNMJFZXG5LFINXW23LFNZ2KUY3PNVWWK3TUL5UWJTVOEFKD4.gif> Message ID: ***@***.*** ***@***.***> >

[bertelschmitt]

Back to my question about missing stream properties, I really need the current frame number and the time in msec. For the frame number, I’m simply pulling it from the cap.iframe property. As cap.count and cap.duration are not used when capturing streams, it would be neat if cap.count reflects the (iframe) framecounter. For the elapsed time in msec, I have no other solution than calculating the elapsed time from the framecounter and the fps. Something like this: self.count = self.iframe self.duration = 1/self.fps*1000*self.count I’m trying to stick this into the code, but have a hard time … Could you? Best, B From: ChenXF ***@***.***> Sent: Friday, May 30, 2025 16:02 To: chenxinfeng4/ffmpegcv ***@***.***> Cc: bertelschmitt ***@***.***>; Author ***@***.***> Subject: Re: [chenxinfeng4/ffmpegcv] False FPS (Issue #70) <https://avatars.githubusercontent.com/u/17546446?s=20&v=4> chenxinfeng4 left a comment (chenxinfeng4/ffmpegcv#70) <#70 (comment)> Thanks for your advisement. Please try this version, I'll release in PYPI next time. pip install -U https://github.com/chenxinfeng4/ffmpegcv.git — Reply to this email directly, view it on GitHub <#70 (comment)> , or unsubscribe <https://github.com/notifications/unsubscribe-auth/AMCPYCTSYJ2JNFCTCVK3GBT3A7677AVCNFSM6AAAAAB5743XLKVHI2DSMVQWIX3LMV43OSLTON2WKQ3PNVWWK3TUHMZDSMRRGQYTSOBTHA> . You are receiving this because you authored the thread. <https://github.com/notifications/beacon/AMCPYCQP7ZKRVKKUAZ33AE33A7677A5CNFSM6AAAAAB5743XLKWGG33NNVSW45C7OR4XAZNMJFZXG5LFINXW23LFNZ2KUY3PNVWWK3TUL5UWJTVOEFKD4.gif> Message ID: ***@***.*** ***@***.***> >

[chenxinfeng4]

This code should work for counting 'elapsed time in msec'.

vid = ffmpegcv. VideoCaptureStreamRT(...)
count = vid.iframe

vid = ffmpegcv. ReadLiveLast(ffmpegcv. VideoCaptureStreamRT, ...)
count = vid.vid.iframe

duration = 1/vid.fps*1000*vid.count

Or you can use the nativetime function of python.

[bertelschmitt]

I know. I am doing something like that at the moment. Suggest sticking it into the code in the next version. Using read frames and elapsed time, the average fps could be calculated on a continuous basis, say every 100 frames, or so ... Some IP cameras change the frame rate during a low light situation .... I have many IP cameras, from weak to powerful, and can test.